In such a device, the expansion chamber and the water box are generally interconnected by an upper passage which constitutes a degassing duct, and by a lower passage which provides a suction orifice. The degassing duct serves to trap bubbles of air or gas in the water box and coming from the cooling liquid and to discharge them into the expansion chamber in order to avoid the risk of "hot spots" in the engine block.
To enable said degassing to operate, the expansion chamber is kept at a lower pressure than the water box by means of suction generated by the cooling liquid flowing out from the water box towards an outlet tube thereform and past the lower or suction orifice or passage.
However, in many practical cases, the outlet tube is sufficiently bulky to require some special orientation to be able to fit in the space available. This can lead to the flow of liquid to the outlet tube creating back pressure rather than suction in the vicinity of the lower or suction orifice or passage. This hinders putting the expansion chamber at reduced pressure and prevents proper degassing of the liquid circulating in the cooling circuit.
Preferred embodiments of the present invention provide a water box and expansion chamber device, preferably in the form of a single moulding, which avoids the above drawback, and in which degassing effectiveness is maintained regardless of the direction in which the outlet tube leaves the bottom of the water box.